The present invention relates to modification of surfaces with polymers and, particularly, to compositions, methods and systems for the modification of surfaces with polymers formed via controlled radical polymerization and for the modification of surfaces with molecules functionalized to initiate controlled radical polymerization.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosure of all references cited herein are incorporated by reference.
Most polymer materials are chemically inert and essentially hydrophobic (that is, they have a passive surface of low surface energy and high contact angle with water and other polar liquids). Therefore, such polymers require surface treatment, for example, to enhance low adsorption of dyes and inks, to overcome inherent low adhesion to coatings and other polymers, to achieve biocompatibility, to impart biocidal activity, or to decrease electrostatic charge effects. Various surface-modification techniques have been widely used in the industry to alter surface properties, including chemical reactions, corona discharge, flame and plasma treatments, and high-energy irradiation. However, most of these approaches require multiple (and often difficult or cumbersome) steps to provide desired functionalization. Moreover, site specific functionalization may be difficult or impossible using such methods.
Nonetheless, polymer surface modification has been a significant issue for many years and is one of the main approaches being studied to introduce new functionalities to existing polymeric materials and thereby improve their performance in practical applications. Indeed the surfaces of solid materials are frequently modified by attachment of polymer films to tailor the surface properties including, but not limited to, color, wettability, biocompatibility, adhesion, adsorption, corrosion resistance, friction etc. However, depending on the final application, different thicknesses of the enveloping polymer layers are targeted to modify the solid surface to attain the desired effect. Polymer films can, for example, be applied by depositing or spraying a polymeric coating from solution. However a robust coating resistant to abrasion and shock is not always attained.
Polymers with reactive groups have also been grafted onto surfaces, resulting in the formation of materials known as polymer brushes. In a number of cases of grafting polymer layers or films onto polymeric surfaces, photoinitiators have, for example, been used. For example, Decker, C. J. et al., Appi Polym Sci 1983, 28, 97 discloses grafting of an acrylate onto polyvinylchloride and polypropylene (PP) films by adding benzophenone as a separate component to the second coating polymer.
A similar two step approach was disclosed in Ruckert, D.; Geuskens, G., Surface modification of polymers, European Polymer Journal 1996, 32, 201-208. In that approach, a “grafting to” polymerization was initiated by a water soluble derivative of benzophenone, Quantacure BTC, which was used to initiate the grafting of acrylamide onto styrene-(ethylene-co-butene)-styrene block copolymer (SEBS).
Likewise, a similar procedure is also disclosed in Decker, C.; Zahouily, K., Surface modification of polyolefins by photografting of acrylic monomers, Macromolecular Symposia 1998, 129, 99-108, in which benzophenone was used as a photoinitiator to generate polymer radicals at the surface of the polyolefin film. The grafting reaction was carried out in an aqueous solution, or with the neat monomer, which was laminated between two PP films.
A procedure to tether a photoresponsive unit to a substrate was disclosed in Samuel, J. D. J. S.; Ruehe, J., A Facile Photochemical Surface Modification Technique for the Generation of Microstructured Fluorinated Surfaces; Langmuir 2004, 20, 10080-10085, in which, a photochemical process was used to allow fluoropolymers to be chemically bound at room temperature onto SiO2 surfaces. A benzophenone silane difunctional molecule was used to form a self-assembled monolayer on the surface of the substrate, which was subsequently coated with the preformed fluoropolymer and irradiated with UV light of wavelength 365 nm. (FIG. 1) See also, Published PCT Patent Application No. WO 2005/083435.
Cho, J.-D.; Kim, S.-G.; Hong, J.-W., Surface modification of polypropylene sheets by UV-radiation grafting polymerization, Journal of Applied Polymer Science 2006, 99, 1446-1461 discloses grafting 1,6-hexanediol diacrylate (HDDA) onto polypropylene (PP) substrates in the presence of benzophenone (BP) and isopropylthioxanthone (ITX) photoinitiators. Subsequently, polyurethane acrylate formulations were coated onto the HDDA-g-PP substrates, using UV radiation.
There are a number of problems with such procedures. For example, one or more of the steps of such procedures may not be environmentally suitable for industrial use. The above-described approaches also require multi-stage procedures for incorporating polymers prepared by non-controlled or free radical polymerization procedures. Addition of multiple components, such as reactive thinner, binder, adhesion promoter, or added low molecular weight photoinitiator are often required in such processes. Further, such processes typically require careful control of reaction conditions and cannot, for example, occur in an open air environment. Moreover, the non-controlled polymerization processes result in formation of non-uniformly responsive surfaces that additionally provide a slow or incomplete response to further stimulation.
Indeed, the control of polymer compositions, architectures, and functionalities for the development of materials with a specific set of properties, such as biological properties, has long been of great interest in polymer chemistry. Atom Transfer Radical Polymerization (ATRP), nitroxide mediated polymerization (NMP), reversible addition fragmentation chain transfer (RAFT) and catalytic chain transfer (CCT) are examples of controlled/living radical polymerization processes (CRP) that provide a relatively new and versatile method for the synthesis of polymers from a broad spectrum of vinyl-monomers with controlled molecular weight, low polydispersity and site specific functionality. Indeed, since CRP processes provide compositionally homogeneous, well-defined polymers (with predictable molecular weight, narrow molecular weight distribution, and high degree of chain end-functionalization) they have been the subject of much study as reported in several review articles. See, for example, Matyjaszewski, K., Ed. Controlled Radical Polymerization; ACS: Washington, D.C., 1998; ACS Symposium Series 685. Matyjaszewski, K., Ed. Controlled/Living Radical Polymerization. Progress in ATRP, NMP, and RAFT; ACS: Washington, D.C., 2000; ACS Symposium Series 768. Matyjaszewski, K., Davis, T. P., Eds. Handbook of Radical Polymerization; Wiley: Hoboken, 2002. Qiu, J.; Charleux, B.; Matyjaszewski, K. Prog. Polym. Sci. 2001, 26, 2083. Davis, K. A.; Matyjaszewski, K. Adv. Polym. Sci. 2002, 159, 1.
CRP processes differ, for example, in the type of group being transferred. For example, ATRP polymerizations typically involve the transfer of halogen groups. NMP polymerizations generally involve the transfer of stable free radical groups, such as nitroxyl groups. Details concerning nitroxide mediated polymerizations are described in, for example, in Chapter 10 of The Handbook of Radical Polymerization, K. Matyjaszewski & T. Davis, Ed., John Wiley & Sons, Hoboken, 2002. RAFT processes, described by Chiefari et al. in Macromolecules, 1998, 31, 5559, differ from nitroxide-mediated polymerizations in that the group that transfers is, for instance, a thiocarbonylthio group, although many other groups have been demonstrated. See, for example, McCormick and Lowe, Accounts of Chemical Research, 2004, 37, 312-325.
ATRP is presently one of the most robust CRP and a large number of monomers can be polymerized providing compositionally homogeneous well-defined polymers having predictable molecular weights, narrow polydispersity, and high degree of end-functionalization. Matyjaszewski and coworkers disclosed ATRP, and a number of improvements in the basic ATRP process, in a number of patents and patent applications. See, for example, U.S. Pat. Nos. 5,763,546; 5,807,937; 5,789,487; 5,945,491; 6,111,022; 6,121,371; 6,124,411; 6,162,882; 6,624,262; 6,407,187; 6,512,060; 6,627,314; 6,790,919; 7,019,082; 7,049,373; 7,064,166; 7,157,530 and U.S. patent application Ser. No. 09/534,827; PCT/US04/09905; PCT/US05/007264; PCT/US05/007265; PCT/US06/33152 and PCT/US2006/048656, the disclosures of which are herein incorporated by reference.
ATRP has been demonstrated to be a versatile technique for the synthesis of well-defined polymers, as well (co)polymers with complex architecture and organic/inorganic hybrid materials. ATRP has, for example, been investigated for the preparation of polymer brushes. The polymer chains of such brushes can be tethered to flat surfaces or curved surfaces, encompassing a range of composition and degree of polymerization (DP). Polymer brushes formed via ATRP can, for example, modify surface properties, prepare nano-pattern displays and/or allow design of stimuli-responsive materials. In a number of procedures for forming polymer brushes, an ATRP initiator is attached to a surface and the polymer chains are “grafted from” the surface.
A drawback of ATRP and other controlled radical polymerizations (CRP) used for polymer brush syntheses in “grafting from” approaches, lies in the inability of CRP techniques to prepare stable, thick polymer layers (for example, in the range of micrometers).
Although a number of advances have been made in the modification of surfaces with polymers, it remains desirable to develop improved compositions, methods and systems to modify surfaces with polymers, particularly wherein the physiochemical properties of the polymer are controlled.